1. Field of the Invention
This invention relates to control of endoergic and exoergic chemical reactions by a photoactive entity. More particularly, the invention relates to photoactive entities, herein called "photochemical diodes", which are capable of operating under the influence of solar radiation to drive endoergic chemical reactions such as the photolysis of H.sub.2 O into H.sub.2 plus O.sub.2 and/or H.sub.2 O.sub.2, and the photolysis of H.sub.2 S into H.sub.2 plus zero-valence S and to control exoergic catalytic chemical reactions.
2. Description of the Prior Art
The photolysis of water into H.sub.2 plus O.sub.2 using solar radiation is of prime importance as a potential new energy scheme which involves a renewable and nonpolluting energy source. The conversion of solar energy into chemical energy has the advantage of easy energy storage (in the form of the photogenerated fuel), as compared with solar energy conversion via photovoltaic or photothermal processes. An important process for accomplishing the decomposition of water into H.sub.2 plus O.sub.2 using solar radiation is photoelectrolysis, such as that disclosed by A. J. Nozik in Vol. 257, Nature, page 383 (1975). However, while the photoelectrolysis process disclosed therein represents a considerable advance in the art, the process, like other photoelectrolysis processes, requires two-dimensional thin-film electrodes distributed over very large areas. In order to make solar energy use more viable, a simplification of the system and a reduction in size is required.
Photocatalysis of chemical reactions is well-known; see, e.g., Th. Wolkenstein, Vol. 23, Advances in Catalysis, D. D. Eley et al. eds., pp. 157-208, Academic Press, N.Y. 1974. However, no practical devices are disclosed.